An ever-expanding field of applications exists for rapid, highly specific, sensitive, and accurate methods of detecting and quantifying chemical, biochemical, and biological substances, including enzymes such as may be found in biological samples. Because the amount of a particular analyte of interest such as an enzyme in a typical biological sample is often quite small, analytical biochemists are engaged in ongoing efforts to improve assay performance characteristics such as sensitivity.
One approach to improving assay sensitivity has involved amplifying the signal produced by a detectable label associated with the analyte of interest. In this regard, luminescent labels are of interest. Such labels are known which can be made to luminesce through photoluminescent, chemiluminescent, or electrochemiluminescent techniques. "Photoluminescence" is the process whereby a material luminesces subsequent to the absorption by that material of light (alternatively termed electromagnetic radiation or emr). Fluorescence and phosphorescence are two different types of photoluminescence. "Chemiluminescent" processes entail the creation of the luminescent species by a chemical reaction. "Electrochemiluminescence" is the process whereby a species luminesces upon the exposure of that species to electrochemical energy in an appropriate surrounding chemical environment.
The signal in each of these three luminescent techniques is capable of very effective amplification (i.e., high gain) through the use of known instruments (e.g., a photomultiplier tube or pmt) which can respond on an individual photon by photon basis. However, the manner in which the luminescent species is generated differs greatly among and between photoluminescent, chemiluminescent, and electrochemiluminescent processes. Moreover, these mechanistic differences account for the substantial advantages as an bioanalytical tool that electrochemiluminescence [hereinafter, sometimes "ECL"] enjoys vis a vis photoluminescence and chemiluminescence. Some of the advantages possible with electrochemiluminescence include: (1) simpler, less expensive instrumentation; (2) stable, nonhazardous labels; and (3) increased assay performance characteristics such as lower detection limits, higher signal to noise ratios, and lower background levels.
As stated above, in the context of bioanalytical chemistry measurement techniques, electrochemiluminescence enjoys significant advantages over both photoluminescence and chemiluminescence. Moreover, certain applications of ECL have been developed and reported in the literature. U.S. Pat. Nos. 5,147,806; 5,068,808; 5,061,445; 5,296,191; 5,247,243; 5,221,605; 5,238,808, and 5,310,687, the disclosures of which are incorporated by reference, detail certain methods, apparatuses, chemical moieties, inventions, and associated advantages of ECL.
Copending and commonly-assigned United States patent application Ser. No. 08/368,429, filed Jan. 4, 1995, the disclosure of which is incorporated by reference, details certain aspects of ECL in connection with beta-lactam and beta-lactamase (neither of which is conjugated through a covalent linkage to an electrochemiluminescent compound).
None of the above-identified documents disclose nor suggest the present invention. Additionally, the practice of the invention offers significant advantages to the skilled bioanalytical chemist in comparison to the electrochemiluminescent techniques taught by these documents. Accordingly, the invention meets the as-yet unmet needs of skilled workers with respect to the achievement of improved assay performance characteristics (e.g., signal output, detection limits, sensitivity, etc.) for the measured species and represents a patentable advance in the field.